(1998) THE ROLE OF GLUCOSE POLYMERS IN RECOVERY FROM EXERCISE IN SLED DOGS ...Arleigh J Reynolds, DVM, PhD, Cornell University, Ithaca, NY Perhaps one of the most overlooked aspects of training is the importance of the recovery period. Recovery has as much or maybe more bearing on an athlete's success as the intensity and duration of exercise performed during workouts. Most of us are pretty conscientious about ensuring our dogs don't miss a workout but we often overlook their need to recover between workouts. Inadequate recovery decreases the benefit an athlete receives from each training session and in extreme cases can increase the risk of developing an illness or becoming injured. To maximise recovery an athlete must be provided with adequate time and nutrition. Like a car's engine, a sled dog requires fuel to run and although certain fuel sources, such as fat, have an almost bottomless gas tank, others like carbohydrates have a rather small tank which requires frequent refills for optimal performance. In the late nineteen sixties a group of Swedish Scientists discovered that human endurance athletes stored more glycogen (the form of carbohydrate fuel stored in the muscle) if they ate a high rather than a low carbohydrate diet. These scientists also found that the increased concentration of muscle glycogen supported by the high carbohydrate diet allowed these athletes to maintain a race pace significantly longer than when they ate a low carbohydrate diet. This research gave rise to the concept of "carbohydrate loading" before endurance events such as the human marathon. While carbohydrate loading has been a very successful strategy for enhancing endurance in human athletes it has not proven as effective for canine athletes. This difference between dogs and people can be explained in part by differences in their ability to metabolise fat. Dogs can support a much greater percentage of their total effort in a race by using fat than can their human counterparts. The most successful strategies for canine endurance have focused on optimising fat metabolism by feeding a high fat diet. This approach slows the rate at which glycogen is used during a race and appears to enhance performance more than storing large amounts of glycogen in the muscles before a race. While fat is quantitatively the most important fuel for sled dogs, glycogen still plays a vital role in race performances. Very intense work such as hill climbing or running at near maximal speeds cannot be supported by burning fat alone. During really hard work glycogen is the preferred fuel. Thus while carbohydrate loading may not work in sled dogs, maintaining adequate levels in this gas tank is essential for an optimal performance. Studies in humans have shown that people eating 500g of carbohydrate a day can completely replete their glycogen stores within 24 hours after one bout of exhaustive exercise. However, when distance runners ran 16 miles a day for 3 consecutive days their pre-exercise muscle glycogen concentration dropped on each successive day so that by the third day they were starting exercise with less glycogen than they had at the end of exerci the first day! When these same athletes were tested after 5 days of rest they had still not repleted their glycogen stores to the normal level they had before the first day of exercise. The studies showed that people working at about the same exerci intensity as a sprint sled dog were unable to maintain normal pre-exercise glycogen concentrations over a 3 day course of exercise and were not completely recovered even after 5 days of rest. After this study was published, exercise physiologists began to examine post-exercise glycogen repletion in hopes of finding a way of helping athletes refill these fuel tanks more rapidly. The first big breakthrough came in the late nineteen eighties when a group from Texas examined the effect of the timing of carbohydrate administration on the rate of glycogen repletion. They discovered that cyclists given a dose of carbohydrates immediately after exercise replaced glycogen twice as rapidly during the first 4 hours of recovery than they did when given the same dose 2 hours after the end of exercise. Later work showed that the greatest rate of glycogen repletion occurs when carbohydrates are given within 30 minutes after exercise ends. There appears to be 2 ways for ingested carbohydrate to get into a muscle cell. The most common way is enhanced by the hormone insulin and will work in a normal animal anytime after it eats a meal containing carbohydrates or protein. During exercise and for the first few minutes afterward carbohydrate can also enter the muscle by a pathway which does not require insulin. Thus if an athlete consumes some carbohydrate during the first few minutes after exercise it can get into the muscle and be converted to glycogen much more rapidly that if the same amount is given more than 30 minutes after exercise. The optimal dose to administer appears to be between 1.5 and 2g of carbohydrate per kg body weight. There is no additional benefit gained from giving more than this amount. Unlike the time of administration, the form of carbohydrate administered does not seem to affect the rate of glycogen repletion. Solid or liquid carbohydrates and simple sugars or complex carbohydrate (such as the starches in cooked rice, bread, and pasta) all support about the same rate of glycogen repletion. Simple sugars sometimes cause a bloated feeling and occasionally lead to vomiting or diarrhoea so the most popular form used by athletes are complex carbohydrates and the most popular form of complex carbohydrates used today are small glucose polymers called maldextrans. These polymers are derived from the digestion of cornstarch and are available in products such as Polyco (trademark from Ross Pharmaceuticals in Columbus Ohio). Within the last 3 years it has been shown that combining the polymers with a highly digestible protein source supports a 15-20% greater rate of glycogen repletion during the first 4 hours of recovery than the polymer fed alone. The protein stimulates the release of more insulin which probably helps get more carbohydrate into the muscle where it can be made into glycogen. These findings have helped human endurance athletes keep their glycogen tanks full, and thus enhance their performance in multiple day competitions. Since most sled dog championships are also multiple day events, this strategy would also help optimi sled dog performance if it works the same in dogs as it does in people. In 1991 a group of Scientists from the Iams Company and myself examined that very question with a group of Rick Swenson's dogs. We took blood samples and muscle biopsies from 24 dogs before exercise and then Rick ran them further and faster that they had been running in training up to that point in an attempt to deplete their glycogen stores. Half the dogs were given 1.5g polycose/kg bodyweight in 500ml of water immediately after exercise, the other half was given only water. The dogs did nearly deplete their glycogen stores during the course of this run. During the first 4 hours of recovery, the dogs treated with polycose replaced about half of the glycogen they consumed during exercise while those given only water showed no significant repletion during the same period. Thus these sled dogs responded to immediate post-exercise carbohydrate supplementation in the same way as the human athletes described earlier. The next step was to try this technique in the field. Over the past three years we have had 6 sprint and 3 endurance teams try this technique during races. In the Sprint teams using polycose, all held or improved their position between the first and second and second and third day of racing. One driver even commented that 2 of his dogs which would not drink the polymer solution after the first day of a race were noticeably more tired coming home on the second day. The distance team drivers remarked that they thought their teams recovered faster and finished stronger with polycose treatment. It must be emphasised that these field evaluations were not controlled experiments and in each case the drivers knew when their animals had been given the polymer and so the "placebo effect" cannot be ruled out. There are so many variables that determine performance that one cannot claim that polymer feeding was the reason for the improvement experienced by the sprint drivers on each successive race day. These evaluations do suggest, however, that polyco supplementation probably did not hamper performance. Based on our earlier study, it is likely that polycose treatment should at least give dogs the fuel they need to perform their best; the actual race outcome depends on the dogs and their driver. During the 1995 season we did some further field evaluations using a polycose/protein mixture. We need to examine this combination under more controlled conditions but the initial feedback from mushers has suggested that a combination may work better than polycose alone. In case you are interested, it costs between $0.75 and $1.00 per dog per day to treat with polycose. We usually dissolve 1.5g polycose/kg body weight in enough baited water so that each dog gets about 1 pint of the solution. We give the dogs the polyco solution as soon as they get back to the truck (or check point) before they are unharnessed or taken from the line. It is crucial that they get it into them as soon after they finish running as possible. As with any other dietary change don't wait for a race to try it; always use it first during a training run so you can make sure your dogs will drink it and it doesn't have any adver effects. We have treated hundreds of dogs without a single complication but it is always safer to try it at least once before you use it in a race. Post-exercise carbohydrate supplementation will not make up for problems with genetics, nutrition, or training. It is a tool that may help your dogs recover a little faster and a little more completely. In the grand scheme it may only improve your time by a second or two per mile, but then again, how many races are won and lost by that margin?